Machine-switching telephone-exchange system



April 1 1924; 1,488,797

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L. POLINKOWSKY MACHINE SWITCHING TELEPHONE EXCHANGE SYSTEM Original Filed Feb. 24, 1919 8 Sheets-Sheet 6 //7 wen for: L/pa Po/M/rawsk y by A April 1 1924. 1,488,797

. i .L. POLINKOWSKY MACHINE SWITCHIiiG TELEPHONE EXCHANGE SYSTEM 0 rigina l Filed Feb. 24, 1919 8 Shet-Sheet 7 MACHINE; SWITCHING TELEPHONE EXCHANGE SYSTEM Original Filed Feb. 24, 1919 '8 Sheet's-Sheet 8 //7 enfan' A 4&4 Po/mkon s/ry Patented Apr, l, 1924.

To all whom it may a citizen of Russia, de Bastion, Antwerp,

stares PATENT FFICE.

LIPA POLIEKGWSKY, 01E ANTWERE, BELGIUM, ASSIGNOR T0 'iTJESTERN ELECTBiC CURVE- PANY, 113T COR-P ORATED, OE NEW YORK, 'N. Y., A. CORPORATION OF NEW YQRK.

.IACHINE-SNJIT CHING TELEPHONE-EXCHANGE SYSTEM.

Original application filed February 24, 1919, Serial No. 278,575. Divided and this application filed Be it k nown that vented certain new and ments in Machineswitchmg Telephone- Exchange Systems in Great Britain up filed Feb. No. 9789/19, filed Jan. 11

land, application 1919; France, ap

Aug. 13,

following act description.

This lnvention relates change systems an wherein machine SW1 employed for the estal tional connections tions is accomplis means of automa is a full, clear,

adopted asthe basis of the successful is automatically actuated ient time to maize the asses the message register.

February 4, 1922.

concern:

I, LIPA POLINKOWSKY, residing at 1% Rue Belgium, have in useful Improvefor which I have filed plication No. Australia, application 1919; No. 41045, filed Jan. 4, plication No. 12177, filed 1919; and Italy, led June 18, 1920),

sees 1s,

New Zeaapplication No. of which the concise, and exto telephone exd especially to systems tching apparatus is olishment of conversabetween subscribers hed entirely or in part by tic switching mechanism, the individual message register is frequently determining the essed against the subscribhers line is equipped with device individual located atthe When a calling subscriber initiates central establishment of ass or kind that involves a servter belonging to his llne at some convensment.

According to the character of the system,

charge a called party responds,

be actuated to successful call at the instant the or its operation may be brought about at any suitable time therec iargeablc against ermitted The time of operating terial and depends solely the switching apparatus ation.

m aj ority recorded on the iere are certain. classes of LblQ to calling lines and ithout charge.

the register of calls made by ther subscribers lines are the calling line and message register, connections availwhich should be Connections es- Serial no. 534,956. 1

tablished to the various types of operators positions, customarily found in central ofiices, belong to these free classes and provision must be made to guard against the actuation of the service meter regardless of whether a call of this class is successfully completed or not. There may also be other types of lines to which service is permitted without assessment against the calling,

party.

A convenient method of accomplishing message registration on subscribers lines is to provide means associated with or in some way related to one of the automatic selective switches used in selectivelyextending such lines. 011 the successful establishment of a call to a line of the class involving a charge said means becomes effective to actuate the calling partys register, whereas, if the call fails to reach completion, said means remains inert and no assessment is rendered. The success of the call is determined by the response of the called party and this fact may be recorded in any suit-- able manner such as to determine the efl'ectiveness of the meter operating, means.

In the case of connections set up to lines of a class which does not entail a service charge some means is required to render the calling subscribers register inefi'ective under all conditions, whetherth call proves successful or not. Where the automatic selector switches are controlled in their successive operations involved in extending a call by some auxiliary controlling device or switch, which may const-itute apart of the organization of the selector itself, may be assigned to the use thereof, or may be operativcly associated therewith in some manner, such auxiliary controlling device serves as a convenient agency for determining'the operation of the message register. Accord ing to the nature of the call being extended the auxiliar switching device is capable of assuming a plurality of different conditions and according to the condition so assumed, the operation of the message register is determined.

Considering a system of the character above described, where the selective switches used for extending connections to lines of different classes are controlled by auxiliary or associated controlling devicesarranged to assume a plurality of conditions, the object of this invention is to provide for the determination of the operation of registers in accordance with the condition assumed by said controlling devices.

A feature of the invention relates to the provision of a system wherein the auxiliary device, which controls the operations of the selective switch, takes up one of a plurality of positions according to the class of the call extended and wherein the effectiveness of the message register is determined in accordance with the position thus taken by said auxiliary device.

Another feature of the invention relates to an arrangement in which an auxiliary control switch, for governing the operations of the selective switch, takes up, during conversation, one position for calls of one class and another position for calls of another class, and wherein the message register is operated if the auxiliary switch assumes one of said positions but remains unoperated when said auxiliary switch assumes the other position. A still further feature relates to a system wherein the auxiliary control switch assumes one position for completing the talking circuit when an operators line is selected and another position when a subscribers line is selected, and wherein the calling line register is operated with the auxiliary switch in its second position but is not operated if the auxiliary switch assumes its first mentioned position. 7

Other features of the present invention will suiiiciently appear from the description of the operation of the circuits and apparatus in the embodiment shown in the ac companying drawings.

Figure 1 shows a subscribers line and a first line finder.

Figure 2 shows a cord circuit comprising a second line finder and a first group selector.

Figures 3 and 4 show a register set and a common arrangement for the timely delay of a monitoring signal.

Figure 5 shows a for local connections.

Figure 6 shows a final selector.

Figure 7 shows a second group selector on the incoming end of a twoovire trunk line.

Figure 8 shows a trunk line extending to a recording or a toll operators position.

Figure 9 shows a trunk line extending to the information desk, complaint desk, wirechiefs desk, etc.

Figure 10 shows a trunk line extending to a distant manual exchange.

This application is a division of my copending application filed February 24, 1919, Serial No. 278,575.

The system disclosed as embodied in the present invention will be best understood from a description of the operation thereof. For an understanding of the general type of second group selector switch employed in this system reference is made to the patent to McBerty N 0. 1,097 ,868, granted May 26, 191 1.

The operation of the circuit of the first line finder, the cord and the final selector is briefly such that, when a line relay 210 is energized, the common starting relays 20 1 provide a. circuit for the energization of the power magnets 211 of the free first line finders in the group- The brush carriages of the free first line finders rotate and in reach ing terminal 210 of the calling line, test relay 21 1- of a line finder is energized and the terminal 210 is made busy through the connection of the low resistance winding of relay 214; and the winding of relay 212 in parallel to the high resistance winding of relay 21 1. Belay 212 disconnects the power magnet 211 and provides a circuit .for the energization of the holding magnet 215 and the common starting relays 216. The brush carriage of the first line finder is arrested, and a circuit is provided for the free second line finders which have access to this first line finder. The second line finders are divided in pairs and when the cords are free the corresponding sequence switches 220 are held either in position 18 or position 1. Only the line finder of a cord on which the sequence switch 220 is in position 1 is able to search for a calling first line finder. Relay 222 of the cord is then energized in a circuit over the front contacts of the common starting relays 216. The power magnet 221 is then energized in a circuit over the front contact of relay 222 and back contact of relay 232 and the brush carriage of the second line finder rotates. On reaching terminal 230 the test relay 23 1 is energized, relay 232 is brought into the same circuit, terminal 230 is made busy, and relay 232 when energized causes the energization of sequence switch 220 in a circuit over front contacts of relays 232 and 222. Sequence switch 220 starts from position 1 and moves into position 4. When sequence switch 220 passes position 2, the high resistance winding of relay 23 1 is disconnected at sequence switch contact 227 bottom, and the energization of relay 23 1'is maintained over its low resistance winding. In position 3 of sequence switch 220 a circuit is established for the energization of relay 235 of the cord, relay 213 of the first line finder and cut-off relay 207 of the calling line, whereby relay 201 is deenergized and the brush carriages of the remaining free first and second line finders are arrested. The release relay 231 together with retardation coil 237 is brought into connection with the calling'line.

In position i of sequence switch 220 the searching sequence energized and a for. Assuming and 1 free,

free register set searched the register set in Figs. 3 a connection with this register switch 280 of the cord is new brought into connection with the secondary winding of dialling tone coil 324: and the stepping relay 325 of the register set. Relay 323 when energized provides over .its front contact and right-hand winding a circuit for the energization of sequence switch 320, which controls the connection of the registers in succession in a circuit which is under the control of the stepping-1n relay Sequence switch 320 starts from position 1 and moves into position 3. In positions 2 and 3 of this sequence switch the primary winding of the dialling tone coil 32a is connected over sequence. switch contact 332 in a circuit with an interrupter 333 and the calling subscriber when receiving the sharp dialling tone winds up the dial to send the first figure of the Wanted number. When sequence switch 320 reaches position 3 relay 323 is deenergized and relay 326 energized in a circuit over back contact of relay 323 and sequence switch contact 327 bottom. The ten thousands register 100 is energized in a circuit over sequence switch contact 328 top, back contact and right-hand winding of relay 329, sequence switch contact 330 top and front contacts of relays 326 and 325. Relay 325 remains thereby deenergized since its left-hand differentially wound winding is connected in a parallel circuit over retardation coil 331. Register 100 starts from position 0 and in closing its local contact 101 provides a shunt around the right-hand winding of relay 329, which is then energized and in opening its back contact disconnects the register. Relay 329 remains energized until the line circuit is opened at the dial and relay 325 is deenergized. Relay 329 in closing its back contact again prepares the circuit for register 100 which receives current as soon as relay 325 is again energized. Over the back contact of relay 329 is also connected in parallel to thev register the relay 337, which when energized maintains-over its front contact the closure of the circuit for relay 329. Relay 337 remains energized until the register reaches its next position and its local contact is opened. On the last interruption at the dial relay 325 remains deenergized for a comparatively long time and the slow operating relay 334 is energized in a circuit over sequence switch contact 342, bottom, and back contact of relay 325. Relay 323 is then energized in a circuit over front contact of relay 334:. Sequence the stepping switch 320 is again energized, starts from position 3 and moves into position 5'. Relay 325 is thereby again energized over the calling line before sequence switch 320 reaches position When the sequence switch passes into position 4: an additional energization of register 100 is provided in a circuit over sequence switch contact 330 bottom, the ten thousands register is then disconnected and the circuit is prepared for the thousand register 110 over sequence switch contact 328 bottom. Relay 326 is deenergized during the time sequence switch 329 moves between positions 3 to 5, and the first energization of register 110 takes place immediately the front contact of relay 326 is closed. Register 110 starts from position 0 and in closing contact 111, the right-hand winding of relay 329 is short-circuited and relay 329 o ens its back contact, and the register competes its step under the control of its contact 111 and is arrested in position 1. Relay 337 is now connected in parallel to register 110 and maintains the energization of relay 329 during the time contact 111 is closed. When the dial is released a second time register 110 is brought to a position corresponding to the figure dialled and sequence switch 320 is advanced from position 5 into position 8 in which the hundreds register 120 is connected in the stepping circuit over sequence switch contact 335 top, and is set up according to the third set of impulses from the dial. Sequence switch 320 is then advanced from position 8 into position 10 in which the tens register 130 is connected in the stepping circuit over sequence switch contact 335 bottom, after which sequence switch 320 is advanced from position 10 into position 12 in which the units register 1 10 is connected in circuit over sequence switch contact 336. When the dialling is complet ed sequence switch 320 is advanced from position 12 into position 1 The capacity of the exchange is assumed to be twenty thousand lines. First and second group selectors and final selectors are therefore provided. lhe register 1G0 register-s the odd and even ten thousands whereas the thousands register 110 controls the selection of the corresponding level at the first group selector. The pcsition of the registers determines the translation from the decimal number system of the wantec. subscriber line to the system or the switches and register determines the translation for the first group selector. The setting up of the first group selector takes place during the time the subscriber continues the dialling and the operation oi the trip spindle of the first group selector is delayed until the first two impulse series are completed on the dial. This corresponds to sequence switch 320 leaving position 5. In position 6 of sequence switch 320 a circuit is closed for the energization of sequence switch 350 over contact 352 top, back contact of relay. 353, contact 103 of register 100 and contact 338 top of sequence switch 320. Sequence switch 350, which controls the connection of the registers in succession for the control of the fundamental circuit of the selectors, starts from position 1 and under the control of its local contact 351 moves into position 3. In position 2 of sequence s *itch 350 the righthand winding of relay 359 is energized in a circuit over hack contact of stepping-out relay and sequence switch contact 354. Relay 359 keeps open, at its back contact, the circuit for resetting the registers.

Assuming that the number of the wanted line is 12453. hen the dial is wound up to digit 1 and then released, the register 100 makes nine steps under the control of the dial and one step under the control of contact 330 bottom. The register 100 is there fore again in its position 0. c On the second digit register 110 has been energized eight times under the control of the dial and is therefore in position 8. When sequence switch 350 reaches position the fundamental circuit is closed over contact 356 top of sequence switch 350, hack contact of relay 357, winding of stepping-out relay 355, contact 358 bottom of sequence switch 350, common wire 296 and winding of relay 222. Both relays 222 and 355 are energized. Sequence switch 220 starts from position 5 and moves into position 6 in which the trip spindle magnet 248 is energized. The trip spindle rotates and produces at its contact 250, top, short-circuitings around the winding of relay 355. As soon as the back con tact of relay 355 is closed the register 110 is energized in a circuit over left-hand hack contact of relay 360, contact 113 of register 110, contact 361 top of sequence switch 350, back contact and left-hand winding of relay 359, back contact of relay 355 and sequence switch contact 354. Simultaneously with the energization of register 110 relay 362 is also energized and provides over its front contact a bridge to the contact of relay 355. Relay 362 in the circuit for the outgoing impulses serves the same purpose as relay 337 in the circuit of the incoming impulses and enables asafe operation of the register. Register 110 starts from position 8 and moves into position 9. In the meantime trip spindle contact 250 has been opened, the stepping relay leaves its back contact, and relay 359 is deenergized. On the following closure of contact 250 relay 355 is again deenergized and register 110 is energized, starts from position 9 and moves into position 0. On the following deenergiza'tion of relay the right-hand winding of relay 357 is energized in a circuit over sequence switch contact 363 top, contact 104 of register 100, contact 114 of mg ister 110, contact 364 bottom and contact 361 top of sequence switch 350, back contact and left-hand winding of relay 359' and back contact of relay 355. Relay 357 opens the fundamental circuit. In parallel to the right-hand winding of relay 357 the sequence switch 350 is also connected and is energized, starts from position 3 and moves into position 4.

l ihen contact 351 is closed and the lefthand winding of relay 359 is short-circuitcd,

this relay is energized and maintains its.

energization over back contact of relay 355. After contact 250 or" the trio spindle is opened, relay 222 is deenergized. Sequence switch 220 starts from position 6 and moves into position 7 inwhi'ch the test relay 234 is connected with the test brush 252 of the first group selector. Relay 222 is now energized in a circuit over conductor 293, back contact of relay 039'21I1Cl contacts 340 top of sequence switch 320. The power magnet 241 of the group selector brush carriage is energized in a circuit over front contact of relay 222. The brush carriage rotates, in the well-known manner, the brushes moving along the terminal row determined by the position of thetrip spindle. In reaching the test terminal leading to a free second group selector, relay 234 is energized in a circuit over test brush 252, contact 401 of sequence switch'420 individual to the second group selector and resistance 402. In parallel to resistance 402 a high resistance release relay 403 is also connected. Relay 234 brings its low resistance winding and the winding of relay 232 in parallel to its iigh resistance winding, and makes the terminal of the group selector busy. Relay 232 is energized, the power magnet 241 is disconnected, sequence switch 220 and the holding magnet 245 of the first group selector are energized, the brush carriage is arrested, and sequence switch 220 starts from position 7 and moves overposition 8 into position 9 in which the fundamental circuit is prepared on sequence switch contacts 247 top and 255 bottom to the second group selector pending the closure of the fundamental circuit at the register set.

Sequence switch 350 remains in position 4 until the third series of impulses at the dial has been completed and sequence switch 320 has left position 3. A circuit is then established for the energization of sequence switch 350 over contact 363 bottom and contact 338 bottom of sequence switch 320. Sequence switch 350 starts from position 4 and moves into position 5. The fundamental circuitcontaining relay of the second group selector is now closed over contact 404 of sequence switch 420, contact 247 of sequence switch 220, contact 286 of sequence switch 280, conductor 296, contact 358 bottom of sequence switch 350, relay 355, back contact of 357, contact 356 bottom of sequence switch 350, right-hand back contact of relay 365, conductor 297 contact 287 of sequence switch 280, contact 255 of sequence switch 220 and contact 405 of sequence switch 420. Both relays 35.) and 422 are energized. Relay 359 is deenergized. Sequence switch 420 is energized in a circuit over its contact 406 and front contact of relay 422. Sequence switch 420 starts from position 1 and moves into position 2 in which the trip spindle magnet 408 is energized in a circuit over sequence and front contact of relay 422. 'The trip spindle rotates and provides at contact 410 top over sequence switch contact 409 shortcircuitings in the fundamental. circuit. The resistance 402 is disconnected at contact 401 from terminal 252 in position 2 of sequence switch 420, and the high resistance relay 403 is left alone in the circuit which includes the test terminal. Relay 234 is de energized and opens its left-hand winding, while relay 403 remains energized over the right-hand winding of relay 234.

When relay 355 is deenergized register 120 is energized in a circuit over contact 122, contact 366 bottom of sequence switch 350 and back contact of relay 359. Register 120 starts from position 6 and moves into position 7, and when register 120 reaches position 0 under the control of relay 355 the register is disconnected, and on the following deenergization of relay 355 a circuit is established over contact 124 of register 120, contacts 361 bottom and 364 bottom of sequence switch 350, contact 114 of register 110, contact 104 of register 100 and sequence switch contact 363 top for the energization of relay 357 and sequence switch 350. The fundamental circuit is opened at the back contact of relay 357 and sequence switch 350 starts from position 6 and moves into its position 9. As soon as contact 410 of the trip spindle is also opened, relay 422 is deenergized and sequence switch 420 is energized in a circuit over its contact 411 top and back contact of relay 422. Sequence switch 420 starts from position 2 and opens the fundamental circuit on the group selector at contacts 404 and 405, contact 404 being opened before contact 358 top of sequence switch 350 is closed. Sequence switch 420 moves into position 5 in which the left-hand high resistance winding of relay 434 is connected over sequence switch contact 413 bottom with the test brush 412. The power magnet 431 of the brush carriage is thereby energized in a circuit over sequence switch contact 414 bottom and back contact of test relay 432. The brush carriage rotates moving the brushes along the terminal row determined by the position of the trip spindle. In reaching the terminals of a free final selector relay 434 is energized in a clrcuit over brush switch contact 407' 412, contact 441 of sequence switch 450 individual to the final selector, and through resistance 442. A high resistance relay 443 is also connected in the circuit. Relay 434 brings its right-hand low resistance winding over its front contact and winding of relay 432 in connection with brush 412 and makes the test terminal to this final selector busy, relay 432 is energized, disconnects at its back contact power magnet 431 and provides a circuit for the energization of sequence switch 420 over contact 406 top and front contact of relay 432. In parallel to the sequence switch over contact 411 bottom is connected the holding magnet 435 of the selector, the brush carriage is arrested and sequenceswitch 420 starts from position 5 and moves into position 10 in which the fundamental circuit is extended over sequence switch contacts 415 and 416 to the final selector. Terminal 412 isnow connected over sequence switch contact 413 top direct with the winding of relay 432, so that the righthand winding of relay 434 is short-circuited and this relay is deenergized.

Sequence switch 350 remains in position 9 until the tens and units registers have been set up under the control of the dial and sequence switch 350 is energized in a circuit over contact 352 top, right-hand back contact of relay 353 and contact 341 bottom of sequence switch 320.

starts from position 9 and moves into posi- Sequence switch 350 tion 10 in which the fundamental circuit is 0 closed at the register set over right-hand back contact of relay 378 and sequence switch contact 379 top. Relay 452 at the final selector and relay 355 at the register set are energized. Relay 359 is deenergized. A circuit is closed for the energization of sequence switch 450 over front contact of relay 452 and contact 490, bottom. Sequence switch 450 starts from position 1 and moves into position 2 in whichthe trip spindle magnet 448 is energized in a circuit over front contact of relay 452. The trip spindle rotates and provides at its contact 455 top short-circuitings of the'fundamenta-l circuit.

When relay 355 is deenergized, register 130 is energized in a circuit over contact 132, contact 367 top of sequence switch 350 and back contact of relay 359. Register 130 starts from position 5 and moves into position 6. After register 130 is restored to position 0 under the control of relay 355 acircuit is established on the following deenergization of relay 355 over contact 134 of register 130 and contact 352 of sequence switch 350 for the energization of the sequence switch and relay 357. The fundamental circuit is thereby opened and sequence switch 350 and moves into position 12. After contact 351 is opened relay 357 is deenergized and the fundamental circuit is again closed at starts from position 10 its back contact. When contact 455 of the trip spindle is also opened relay 452 is deenergized and sequence switch 450 is energized in a circuit over back contact of relay 452 and contact 491, top. Sequence switch 450 starts from position 2 and moves into position 5. The duration of the opening of the fundamental circuit at back contact of relay 357 is so selected that contact 447 of sequence switch 450 is opened before relay 452 can be energized. a second time over the fundamental circuit whereas the energize-- tion of this relay takes place before sequence switch 450 reaches position 5. The power magnet 461 of the brush carriage is now energized in a circuit over contact 492,

top, and the front contact of relay 452.

The brush carriage rotates 'moving the brushes along the sixth terminal row and. a series of short-circuitings of the stepping relay 355 in the fundamental circuit is'again produced at contact 457 top of the brush carriage.

WVhen the relay 355 is deenergized a circuit is established for the energization of register 140 over contacts of relays 355 and 359, contact 367 bottom of sequence switch 350 and contact 142 of units register 140. After register 140 reaches position 0 under the control of relay 355 a circuit is established for the energization of sequence switch 350 and relay 357 at the following deenergization of relay over contact 143 of register 140, back contact of relay 374 contact 144 of register 140 and contact bottom of sequence switch 350. The fundamental circuit is again opened and sequence switch 350 starts from position 12 and moves over positions 15, 16 and 17 as will be hereinafter described) into position 1. In position 13 of sequence switch 350 a circuit is established for the energization of relay 339 over contact 368 bottom of sequence switch 350, left-hand back contact of relay 365 and sequence switch contact 369. The energization of relay 339 causes the deenen gization of relay 222 in the cord, whereby sequence switch 220 starts from position In position 10 of the sequence switch 220 the fundamental circuit of the register set is disconnected. Supervisory relay 262 and retardation coil 257 are connected to the final selector. When sequence switch 220 leaves position 9 the subscribers line is again connected with relay 231 and retardation coil 237. In position 10 sequence switch 220 is energized in a circuit over back contact of relay 262. Sequence switch 220 moves over position 10 into position 11.

As soon as relay 325 at the register set is deenergized sequence switch 320 is energized in a circuit over contact 348 bottom and back contact of relay 325. Sequence switch 320 starts from-position- 1 4 moves into position 15. When sequence switch 350 reaches position 1 a circuit is established for the energization of relay 323 over contact 322 bottom of sequence switch 320 and contact 369 bottom of sequence switch 350. Sequence switch 320 is again energized over front contact of relay 323 starts from position 15 and moves into position 17 in which relay 334 is energized in a circuit over sequence switch contact 342 top, back contact of relay 326 and sequence switch contact 340 bottom. Relay 323 is again energized over front contact of relay 334, sequence switch 320 is energized over front contact of relay 323and starts from position 17 and moves into position 1.

After the fundamental circuit has been opened at the register set the relay 452 is deenergizedas soon as contact 457 top is opened, the power magnet 461 is disconnected and sequence switch. 450 is energized ina circuit over each contact of relay 452. The holding 'magnet 465 is connected in parallel to the sequence switch. The brush carriage is arrested and sequence switch 450 starts from position 5.

hen the sequence switch of the final se lector reaches position 8 the wanted line undergoes a test and the right-hand high resistance winding of test relay. 464 is connected in a circuit over the cut-oif relay of the wanted line. If the line is free relay 464 brings into circuit over its front contact, its left-hand low resistance winding together with winding of relay 462 in parallel to its high resistance winding. The terminal of the wanted line is so made busy whereas relay 462 is energized. Sequence switch 450 in r ,aching positionv 10 is energized. in the circuit over front contact of relay 462 and moves over positions 10 and 1 into position 12 in which an alternating ringing current is immediately sent to the station of the wanted line. Relay 452 is brought into connection with a common interrupter 469,. which when closed causes the energization of said relay which at its, front contact com: pletes a circuit to move sequence switch 450 into position 13. in which relay 452 is connected with a further common interrupter 4.72. The two interrupters 469 and 472 are continuously operated and are a"; angcd to close th circuit to ground at predetermined intervals so that after the sequence switch 450 reaches position 12 it is brought, after the lapse of a few seconds, over positions 12 and 13 into position 14.

When sequence switch 450 reaches position 14 the direct connection of the ringing current is removed and the the subscribens line alternately with the source of ringing current and ground is maintained over for the usual intervals by means of interrupter 474. During the time sequence switch 450 is in positions 12 to 14 the primary winding of tone coil 477 is conconnection of nected to a common interrupter, and the secondary windings of coil 477 are connected in bridge to the line. The calling subscriber perceives an indication that the ringing or the called party is proceeding. As soon as at the wanted station the receiver is lifted from the hook the ringing relay 460 is energized and causes over its front contact the energization of sequence switch 450 which starts from position 14 and moves into position 15 in'which a through connection of the called subscribers line is made to the transmitter current supply bridge at the first group selector. Relay 262 is energized. Sequence switch 220 starts from position 11 and moves into position 12.

if the number of the wanted subscriber begins with the. figure 2 and the wanted number is, for example, 22453, the ten thousands register 100 is finally set in position 9. When the fundamental circuit is closed over relay 222 of the first group selector the thousands register 110 is first restored to position 0 and then the tenthousands register 100. The trip spindle of the first group selector makes an additional step. The brush carriage of the first group selector searches now in an even level for a tree trunk line to a distant exchange. On the incoming end of the trunk line'is provided a second group selector as shown in Figure 7. The fundamentalcircuit when extended to the first group selector over the sequence switch contacts 247 and 255 is closed on the distant end of the two-wire trunk line at the contacts 504 and 505 through relay 522 of the second group selector to ground. Sequence switch 520 is thereby energized over contact 506 and front contact of relay 522, starts from position 1 and moves into position 2 in which the trip spindle 508 is energized in a circuit over sequence switch contact 507 top and-front contact of relay 522. The trip spindle rotates and at its contact 510 top over sequence switch contact 509 bottom provides short-circuitings for the fundamental circuit. After the fundamental circuit is opened both at the register set and at contact 510 of the trip spindle relay 522 is deenergized and sequence switch 520 is energized in a circuit over contact, 511 top and back contact of relay 522. Sequence switch 520 starts from position 2and moves into position 5 in which the power magnet of the brush carriage 531 is energized ina circuit over sequence switch contact 514 bottom and back contact of test relay 532. The. left-hand high resistance winding of the other test relay 534 is'thereby connected over sequence switch contact 513 bottom to test brush 572. The brush carriage rotates moving the brushes along the terminal row determined by the position of the trip spindle and searches for a final selector such as shown in Figure 6. When the final se= lector has been found relay 534 is energized and the test terminal of the final selector is made busy. Also relay 532 is energized an d'sequence switch 520 is energized in a circuit over contact 506 bottom and front contact of relay 532. During the time sequence switch 520 remains in position 5 both windings of the release control relay 523 together with the retardation coil 524 are brought in bridge of the trunk line over sequence switch contacts 504 top and 505 top.

Sequence switch 350 at the register set in the exchange, after the control of the fundametail circuit for the second group selector is completed, moves as has been described into position f). A. circuit is established over sequence switch contact 358 top and 356 top through relay 377 ,which together with relay 523 in the distant exchange, is energized in a metallic circuit over the trunk line before sequence witch 350 reaches position 3. Relay 353 is energized in a circuit over front contact of relay 377 and contact 370 of sequence switch 350. Relay 353 maintains its energization over its'left-hand front contact independent of sequence switch contacts 370 and openson its righthand back contact the connection with sequence switch contact 352 so that sequence switch 350 is disconnected in position 9. When the sequence switch 520 on the second group selector in the distant eX- change is energized over front contact of relay 532 and leaves position 5.; the circuit over the trunk line is opened at the sequence switch contacts 505 and 504 during the time sequence switch 520 moves over position 6. In positions 7 and 8 of sequence switch 520 the circuit including relay 523 isagain closed. The opening of the trunk line causes the deenergization of relay 377 and in consequence of relay 353, but as soon as the trunk line is again closed relay 52 3 is again energized, sequence/"switch 520. is arrested in position 8 and remains there waiting until sequence switch 350 of the register set becomes energized in the circuit over contact 341 of sequence switch 320, which can take place when the dialling has been completed and sequence switch 320 is advanced into position 14. .When sequence switch 350 leaves position 9 the circuit containing the battery and relay 377 is broken at contact 358 top and 356 top. l-lelay 523 is deenergized and sequence switch 520 is energized in a circuit over its con.act 506 top and back contact of relay 523. s

Sequence switch 520 starts from position 8 and moves into position 10. When passing position 9 a circuit is closed for the energization of relay 452 of the final selector over contact 444 of sequence switch 450, contact 515 bottom and contact 517 of'se- 'ouence switch 520 so that relay 452 causes the energization of sequence switch 450 and its starting from position 1. Sequence switch contact 516 is closed before sequence switch contact 517 is opened and the circuit is extended to the relay 355 of the register set in the exchange after which the final selector is set up under the control of the tens and units register, as has been described, and it has been secured that the second group selector on atwo-wire trunk cannot produce the starting impulse for the sequence switch of the final selector unless the register set is ready to control the final selector, while the register set prevents the preparation of the fundamental circuit until a free trunk line to a final selector has been selected. when the sequence switch 450 of the final selector leaves position 5, resistance 442'is disconnected at contact 441 and the high resistance winding of relay 443 is left alone in the circuit of relay 532, which is thereby deenergized. Sequence switch 520 is thereby energized in a circuit over contact 514 top and back contact of relay 532. Sequence switch 520 starts from position, 10 and moves into position 15 in which relay 523 is again brought in bridge to the trunk line, while supervisory relay 525 together with retardation coil 526 is brought over sequence switch contacts 515 and 516 in connection with the final selector.

The closure of contacts 368 bottom of sequence switch 350 on the register set is so timed that sequence switch 220 of the cord is advanced into position 10 after the sequence switch of the final selector has left position 5 and has opened its contacts 444 and 445, while sequence switch 220 reaches position 10 before sequence switch 520 of a group selector on the end of a two-wire trunk reaches its position 15 so that relay 523 is energized in a metallic circuit over relay 262 and retardation coil 257. When the called subscriber answers and the sequence switch of the final selector moves into position 15 the transmitter current supply to the called station is provided over relay 525 and retardation coil 526, and relay 525'is energized and provides a shunt around the high resistance winding of relay 523. Relay 262 is thereby energized and sequence switch 220 advances into position12.

If the second figure of the wanted number is odd, the first group selector is set up to a level. as if the lower even figure has been dialled, whereas the second group selector is advanced to another level producing thereby the second translation on the switches. Assuming that the number of the wanted sub scriber was 13453, register 110 receives seven impulses and is arrested in position 7. When sequence switch 350 moves over'posi tion 2 relay 360 is energized in a circuit over contact 116 of register 110, contact 371 bet 7 tom and contact 351 of sequence switch 350.

Relay 360 maintains its energizati'onover its right-hand front contact and sequence switch contact 372 top. Over the left-hand contact of relay 360 the circuit for register 110 is so modified that this register when under the control of the stepping relay 355 is arrested in position 9 instead of position 0. The circuit therefore when next closed extends over back contacts of relay 355 and relay 359, contact 361 of sequence switch 350 and contact 113 of register 110, lefthand front contact of relay 360, contact 115 of register 110 and contact 104 of register 100 to the sequence switch 350 and relay 357. The trip spindle of the first group selector takes therefore the same position whether numeral 2 or numeral 3 has been dialled for the second figure of the wanted subscribers number. After sequence switch 350 leaves position 3 relay 360 is deenergized and when in position 6 of the sequence switch 350 the register 120 is brought to position 0 under the control of relay 355, the circuit at contact 124 of register 120 is first extended over sequence switch contact 361, contact 112 of register 110 and'back contact of relay 360 to the register 110 which on the following deenergization of relay 355 is restored to its position 0 while the next subsequent deenergization of relay 355 causes the opening of the fundamental circuit. Each time the second digit dialled is odd the trip spindle of the second group selector makes therefore an additional step.

If the third digit of the wanted number is odd, as for example the number 12553, register 120 receives from the dial five impulses and is arrested in position 5. lVhen sequence switch 350 moves over position 411;

rela s 373 and 374 are ener ized in a circuit over contact 375 top of sequence switch 350 and contact 126 of register 120 whereby relay 373 provides a locking circuit over its front contact and sequence switch contact 372 bottom. After the units register 140 has been set up the energization of relays 373 and 374 is maintained over contact 146 of register 140 and contact 369 of sequence switch 350. When sequence switch 350 passes over position'5 register 120 is energized in a circuit over its contact 122, contact 366 top of sequence switch and contact 126 of register 120. Register 120 makes an additional step and takes the same position as if the next lower even digit had been dialled. The trip spindle of a second selector takes therefore the same position disregarding whether the third figure of the wanted number was even or odd, and relay 374 controls the translation for the units of the final selector, causingthe advance of the brush car riage to the second" half of the terminal row. 7 When the brush carriage of a final selector moves between the first and second half of the terminal arc the short-circuiting contact 457 of thebr'ush carriage" isin the wellknown manner closed for a comparatively longer time and if the wanted number corresponds to the first terminal in the second half of a terminal arc, the long closure of contacts 457 is delaying the starting of sequence switch 450 and opening of contact 444. In order that the sequence switch 220 of the cord shall not move into position 10 before contact 444 is opened at a final selector, the circuit at the register is so arranged that if the wanted number is the first in the second half of the terminal are of a final selector, the energization of relay 839 and in consequence the deenergization of relay 2-22 is correspondingly delayed. The first terminal on the second half of the terminal arc corresponds to an odd position of register 120 and 0 position of register 140. if therefore relay 373 has been energized on an odd position of register 120 and if register 140 has received ten impulses from the dial and is arr'esttd in its position 0, a circuit is closed in position 10 of sequence switch 350 for the energization of relay 365 over contact 145 of register 140, contact 37 5 bottom of sequence switch 350. front contact of relay 37 3 and sequence switch contact 372 bottom. Relay 365 once energized maintains its energization over its left-hand front contact and sequence switch contact 369 top. When, after the completion of the selection sequence switch 350 reaches position 13, the circuit for relay 339 is maintained opened at the left-hand back contact oi relay 365 and this circuit is closed in position 14 of sequence switch 350 over the sequence switch contact 368 top, front contact of relay 365 and sequenceswitch contact 369.

When, after a conversation the calling subscriber restores his receiver on the hook, relay 231 is deenergized and sequence switch 220 starts from position 12 and moves over position 13 into posit-ion 17. When sequence switch 220 moves over positions 14 to 16 a circuit is closed from the metering battery 259, contact 286, bottom left-hand back contact of relay 224, winding of relay 235, terminal 238, winding of relay 213, winding of message register magnet 208 to battery. The ma net 208, being marginal, has not operated up to this time, but the inclusion of the metering battery 259 in the circuit increases the potential and causes the actuation of said magnet. In position 17 of sequence switch 220 the magnet 241 is energized and the brush carriage rotates until its home contact 269 is reached, when relay 232 is energized in a circuit over contact 269. The brush carriage is arrested and sequence switch220 starts from position 17 and moves into position 18.

After sequence switch 220 leaves posi tion 12 the brushes of the first group selector are disconnected if the connection has been established over a local second group selector, as shown in Figure 5, relay 403 is deenergized and sequence switch 420 is energized in a circuit over sequence switch contact 417 and back contact of relay403. Sequence switch 420 starts from position 10 and moves over position 15 into position 17 in which power magnet 431 is again energized in the circuit over sequence switch contact 414 and back contact of relay 432, and the brush carriage of the group selectoris restored to its position of rest, and when the home contact 493 is closed, relay 432 is energized in a circuit over contact 493 and sequence switch contact 401 top. The power magnet 431' is disconnected on the back contact of relay 432 and sequence switch 420 is energized in the circuit over the front contact of this relay. In parallel to sequence switch 420 is connected over its contact 411 the holding magnet 435, the brush carriage is arrested whereas sequence switch 420 starts from its position 17 and moves into its position 1.

After sequence switch 420 leaves position 15 and its contact 413 top is opened, relay 443 the final selector is deenergized and sequence switch 450 startsfro-m position 15 and moves into position 17. Relay 452 is brought over sequence switch contact 466 bottom in connection with the called line, and if the called subscriber has not restored his receiver to the hook relay 452 is energized, sequence switch 450 is held in position 17 and lamp 481 displays a guarding signal. restored his receiver, relay 452 is deenergized and sequence switch 450 starts from position 17 and moves into position 18 in which the brush carriage rotates until its home contact 457 bottom is closed, whereupon relay 452 is energized; the brush carriage is arrested and sequence switch 450 starts from position 18 and moves into position 1.

If the connection has been established over a two-wire trunk to a distant exchange, the selector shown in Figure 7 has been used, and relay 523 on the selector is de energized as soon as front contact of relay 231' is opened in the outgoing exchange.

Relay 522 is thereby energized in a circuit over sequence switch contact 509 top and back contact of relay 523. Sequence Switch 520 is then energized in the circuit over contact 506 bottom and front contact of relay 522. Sequence switch 520 starts from position 15 and moves into position 17 in which the brush carriage is restored to its position of rest, after which sequence switch .520 moves into position 1. A comparison of the second group selectors in Figure 5 and in Figure 7 will show that the contacts of the sequence switches 520 and 420 have the same arrangement and that only the circuit of the selector is modified, so that a local second group selector can at any time if needed be converted into a two-wire trunk group selector and vice versa.

After a release of a connection sequence switch 220 of the cord remains in position 18 until the second cord of the pair of cords is engaged in a call.

If the called subscriber'is the first to restore his receiver on the hook, relay 262 in the cord is deenergized and sequence switch 220 is energized in a circuit over back contact of relay 262. Sequence switch 220 starts from position 12 and moves into position 13. The circuit over the brushes of the first group selector is thereby disconnected, the second group selector and the final selector are released, and the sequence switch of the cord remains in position 1.3 with the calling line held busy until the calling subscriber restores his receiver and relay 231 is deenergized.

If the wanted line has been found busy and the test relays 464 and 462 have not been energized when sequence switch 450 of the final selector moves over position 8, the sequence switch 450 is arrested in position 10. The secondary winding of the busy tone coil 477 is thereby brought in bridge to the line and the calling subscriber receives a busy toner WVhen the subscriber restores his receiver and relay 231 is deenergized a circuit is established for the energization of the left-handwinding of meterhindering relay 224. Relay 224 disconnects at its left-hand back contact the circuit for relays 235, 213 and 207, and a holding circuit is provided over the left-hand front contact of relay 224 for its left-hand winding. Over the right-hand front contact of relay 224 and its right-hand low resistance winding, a circuit is established for the energization of sequence switch 220. Sequence switch 220 starts from position 11 and moves over positions 12 and 13 into position 17. VAfter the disconnection of the group selector the second group selector is released, as has been described, relay 443 at the final selector is deenergized and sequence switch 450 starts from position 10 and moves into position 11 in which the brushes are restored to their position of rest, where after contact 457 bottom is closed, relay 452 is energized. Sequence switch 450 starts from position 11 and moves into position 1.

Since sequence switch 220 is held in position 11 whether the wanted line is busy or a ringing current is sent to the wanted station, relay 224 is energized if the calling subscriber gives up the connection before the called subscriber has answered. The release proceeds therefore without metering if the sequence switch of the final selector is in its ringing position and the called subscriber does not answer.

A connection can be immediately released new? at any stage of the progress of the selection. Briefly stated, the operation is such that on a release started before the cord obtains a connection with a free register set, the meter-hindering relay 224 is energized and frees the calling line, sequence switch 220 is held in position 4 until sequence switch 280 reaches a free register set and relays 234 and 232 are energized, or until sequence switch 280 passes position 9!; and sequence switch 220 is energized in a circuit over contact 289 of sequence switch 280 and right-hand front contact of relay 224. Se

quence switch 220 then completes its rotation. When the release is started as soon assequence switch 220'is in position 5 and before the fundamental circuit is closed at the register set, relay 339 is energized in a circuit over back contact of the stepping Vrelay 325 when sequence switch 320 passes started and relay 222 is deenergized at the time sequence switch 220 is in position 9, V

the sequence switch moves over positions 9 and 10 into position 11 in which relay 224 is energized. In all these premature releases the operation of the meter 208 on the calling line is prevented through the disconnection of the metering battery 259 at the left-hand back contact of relay 224.

When the release is started before the dialling is completed, relay 339 is energized in one of the posit-ions 4fl, 7:}, 93; or 11- of sequence switch 320, and when the connection is given up at the calling subscribers station after the wanted number has been dialled but before the selection is completed, sequence switch 320 is energized in position 14 over contact 348 bottom and back contact of relay 325. In position 15 relay 339 is energized in the circuit over sequence switch contact 348 top "and back contact of relay 325, so that relay 222 in the cord is deenergized. During the premature release of the register set sequence switch 350 is moved without delay over the positions in which the fundamental circuit of the selectors can be closed. Nhen' sequence switch 320 reaches position 15 sequence switch 350 is energized 'in a circuit over contact 371 top and contact 346 bottom of sequence switch 320. Sequence switch 350 moves from the position in which the premature release started over position 12 into position 15 in which a check is made to determine whether or not the registers 120, 110 and 100 are in their positions of rest. At contact 343 of sequence switch 320 the back contact of relay 359 is connected to ground and the circuit is established for the resetting of the registers, should they not be in position 0, over contact 343 of sequence switch 320, contact 366 of sequence switch 350and contact 122 of register 120. After register 120 reaches position 0 a circuit is extended over contact 124 of register 120 and contact 361 of sequence switch 350 to register 110 and after this register is in its position 0 the circuit is extended over contact 364 of sequence switch 350, contact 114 of register 110 to register 100.. After this register is in position 0 the circuit is extended over contact 104 and sequence switch contact 363 to sequence switch 350. Sequence switch 350 then starts from position 15 and moves into position 16 in which a check is made to determine whether or not thetens register 130 is in position 0, and a circuit is established over contact 343 of sequence switch 320, contact 367 of sequence switch 350 and contact 132 of register 130. After this register is in position 0, the circuit is extended to sequence switch 350 which is then energized over contact 252 and contact 134 of register 130.- Sequence switch 350 starts from position 16 and moves into position 17 in which a check is made to determine whether or not the units register 140 is in position 0. A circuit is established over contact 343 of sequence switch 320 "and! contact 367 bottom of sequence switch 350 to register 140. When register 140 is in position 0 the circuit is extended over contact 143, back contact of relay- 374, contact 144 of register 140 to sequence switch con tact 352. Sequence switch 350 starts'from position 17 and moves into position 1 in which relay 323 is energized, as has been described.

When a release is started and relay 222 is deenergized at a stage in which sequence switch 220 of the cord is in position 7 relay 224 is energized as soon as sequence switch 220 reaches position 8. The sequence switch remains in position 8 until the brush carriage is restored to its position of rest. Relay 222 remains connected over sequence switch contact 246 top to conductor 293. It is therefore desirous that the register set shall not be given free andv shall not be taken for a new. call until contact 246 of the cord which has been released is opened. If the sequence switch 320 reaches position 17 before contact 246 of sequenceswitch 220 is opened, a circuit is established for the energization of relay 326 over back contact of relay 323, contact 327 top of sequence switch 320, wire 293,contact 246 top of sequence switch 220 and winding of relay 222. Sequence switch 320 is held in position 17 until relay 326 is deenergized.

When a release is started during the progress of a selection on which a local second group selector, as shown in Figure T is used, relay 403 is deenergized as soon as relay 224 is energized and its right-hand back contact is opened. Then the release is started at the time the fundamental circuit is closed on the register set for the setting up of the trip spindle of the second selector, sequence switch 350 is in position 6 and the left-hand winding of relay 357 is energized in a circuitover contact 376 bottom of. sequence switch 350 and right-hand front contact of relay 339.

lay 422 at the second group selector is deenergized and sequence switch 420 starts from position 2. Before sequence switch 420 reaches position 5, relay 222 in the cord is already energlzed and relay 403 is deenergized. In position 5 of sequence switch 420 its energization is maintained over back contact of relay 403, whereby the holding magnet 435 is also energized and the brush carriage is held in position of rest. In position 6 of sequence switch 420 relay 432- is energized in the circuit over the home con tact 493, and the energization of sequence switch 420 is maintained in position 6 over front contact of relay 432. Sequence switch 420 then completes its rotation and is arrested in position 1. If the release is started and relay 403 becomes deenergized at the time sequence switch 420 is in position 5 in which the circuit for searching of a free terminal to a following selector is closed, sequence switch 420 is energized over back contact of relay 403 and moves immediately over position 5 into position in whichthe power magnet 431 is maintained energized and the brush carriage is restored to its position of rest without the testrelay 434 testing the terminals. When the contact 493 is closed, relay 432 is energized and sequence switch 420 moves out from position 6 and completes its rotation.

If the release is extended to the second group selector after a connection with the terminals of a free final has been obtained and sequence switch 450 has left position 1 through the closure of the fundamental circuit in the register set. relay 452 remaining deenergized for a longer interval enables seuence switch 450 to pass over positions 2 and 5 and to disconnect resistance 442 before the sequence switch 420 of the second group selector leaves position 15, and terminal 412 is given free, so that the high resistance relav 443 hinders the connection of another second group selector until sequence switch 450 has completed its operation and reaches position 1.

: When a release is started and the fundamental circuit is opened at the time the brush carriage of a final selector is rotating under the control of the register set along the terminals of the subscribers lines, it is The fundamental circuit is opened at the back contact of relay 357, re-

essential that during the release a subscribers line shall not be disturbed through sequence switch 450 completing its rotation. Sequence switch 420 at such a premature release is always advanced over position 15 before sequence switch 150 reaches position 11, so that relay 462 is deenergized through opening of the front contact of relay 443 and the brush carriage of the final selector is restored in position 11 of the sequence switch in the same manner as has been described in the case of the calling line being found busy. In this way the release of the sequence switch of a final selector is accon'iplished without disturbing the subscribers line on which the brushes may "happen J to stay, whenever the release is started before the selection under the control of the register set is completed. Of special importance are releasesduring the progress of a selection over a two-wire trunk line to a distant exchange. The fundamental circuit at the register set may be opened during the time sequence'switch 520 is in position 2 and sequence switch 350 on the register set is in position 6. V The fundamental circuit is opened immediately and relay 357 is energized in a circuit over se quence switch contact 37 6 bottom and front contact of relay 339. This detern'iines the moment of opening of the fundamental circuit independent of the position of sequence switch 320. Sequence switch 520 on the incoming end of the trunk line, when started from position 2 will reach position 5 before sequence switch 350 leaves position 6, unless the restoration of registers 120 and 110 has been already completed, because the circuit for registers 120 and 110 and sequence switch contact 350 is held opened at the back contact of relay 359 until sequence switch 320 reaches position'l 5 and closes contact 343 bottom. Relay 523 is deenergized when sequence switch 520 reaches position 5 and relay 522 is energized in the circuit over sequence switch contact 509 top andback contact of relay 523. Sequence switch 520 is energized over frontcontactof relay 522, leaves position 5 and moves into position 6 in which relay 532 is energized over contact 539, maintaining the energization of sequence switch 520 which completes its rotation. If the subscriber has completed the dialling but the selection has'been delayed at the first group selector and the release is started at the moment sequence switch 320 is in position 15, while sequence switch 350 is in position 6, sequence switch 520 does not reach position 5 before contacts 358 top and 356 top of sequence switch 350 are closed. Relay 523 on the second group selector is thereby energized and the brush carriage can start to rotate. The sequence switch 350 leaves position 9 and relay 523 becomes deenergized before the brushes are able to reach the first terminal. Sequence switch 520 will then be energized, as has been described, and moved into position 6 in which the brush carriage is restored to its position of rest.

\Vhen the release starts at some later time during which the brush carriages of the second group selector are rotating, the deenergization of relay 523 through sequence switch 350 leaving position 9 may happen at the instant a free terminal of a final select-or is reached, Relay 534- becoines energized and the terminal is made busy. Se-

7 quence switch 520 is arrested in position 10.

The energization of relay 152 of the final selector over the passing contact 517 of the sequence switch 520' prevents a hanging up of this sequence switch, in that sequence switch 450 of the "final selector starts from position 1 and in passing positions 2 and 5 disconnects resistance 4A2 and causes relay 532 to deenergize. Sequence switch 520 starts from position 10 and the second group selector is released. The energization of relay 224 of the cord: is at such a release slightly delayed in that relay 222 is maintained energized over contact 380 of sequence switch 350, left-hand back contact of relay 378 and sequence switch contact 369 until sequence switch 350 passes position 1 2. This makes it certain that the out going end of a two-wire trunk is maintained busy until the sequence switch of the final selector has passed position 5 so that rela 4-52 could not be energized over the twowire trunk line and the fundamental circuit of a new call. V

\Vhen the dial at the subscribers station is set up to a higher number than the capacity of the exchange, and the first figure dialled is different from Figures 1 or 2, the register 100 in the exchange takes a position different from position 9 or 0. If the subscriber does not notice hismistake he obtains. a connection in the exchange over a special line'with the supervisory operator who calls the attention of the subscriber to the error made. If register 100 takes a position different from positions 9 or 0, sequence switch-350 cannot start from position 1 after sequence switch320 reaches position 6 since the circuit for the energization of sequence switch 350 is maintained opened at contact 103 of register 100. The other registers are moreover prevented from receiving impulses from the stepping relay 325 through opening of contact 105 on register 100, and these registers remain in position 0, and after each series of impulses from the dial, relay 334 is energized and the sequence switch 320 is advanced to its next position. After the subscriber completes the dialling and sequence switch 320 moves into position 14, sequence switch 350 is energized :in a circuit over contact 352, back 

